Inductive charging (also known as “wireless charging”) uses an electromagnetic field to transfer energy between two objects. This is usually done with a charging station. Energy is sent through an inductive coupling to an electrical device (typically a portable device), which can then use that energy to charge batteries (or run the device).
Inductive charging uses a transmitting induction coil to create an electromagnetic field from the charging station, and a receiving induction coil in the electrical device takes power from the electromagnetic field and converts it back into electrical current to charge the battery. The two induction coils in proximity combine to form an electrical transformer.
Inductive charging of electrical devices such as phones and accessories (smartbands, watches, hearing aids, small loudspeakers, etc.) is an emerging technology and today 3 standards exists, namely A4WP, Powermat and Qi.
Common to all standards is that they use electromagnetic field transmission generated by a flat or a conventional coil and the field is then received by a similar flat coil in the device which has a rechargeable battery installed. The transmitting and receiving coils of such systems needs to be aligned such that the electromagnetic field transmitted get picked up by the receiving coil and for two flat such coils this means the receiving coil needs to be put on top and parallel to the transmitting coil for maximum energy transfer. If the receiving coil is put for example perpendicular to the transmitting coil no energy can be transferred. Practically it has been demonstrated that the A4WP resonance system can allow up to 5 cm distance between the coils for efficient power transfer for a 25 cm2 sized coil area. Turning the receiver coil vertically when the transmitting coil is horizontally oriented cuts the charging off as no magnetic flux can be picked up in this situation.
Hence, alignment of the receiving and transmitting coils is important for inductive charging. However, such alignment might be difficult to achieve.